1. Field of the Invention
The present invention relates to an electronic photograph developer, more specifically to that used in a heat depositing method.
2. Description of the Related Art
In general electric photograph copying devices, toner is applied on a latent image on the photosensitive drum to form a visible image from the latent image. This visible image is transferred on a piece of transfer paper or the like, and then fixed thereon to obtain a copy image. There are two techniques, heat and press fixings to fix a transcription image. The heat roller fixing technique, in which toner is melted by its heat and then fixed on a sheet, is widely used.
This heat roller fixing technique, however, includes the problem of a so-called offset phenomenon, in which fogging is created on the image-transcribed material by toner attached thereonto from the surface of the heat roller. This offset phenomenon can be divided into low-temperature and high-temperature offsets. The low-temperature offset occurs when toner is not completely fixed onto the sheet because of a fixing temperature, which is insufficiently low. The high-temperature offset occurs when the internal cohesive force in the melted toner becomes weaker than the adhering force working between the fixing roller and the sheet.
Covering the roller surface by a material having a toner-releasing property, such as fluorine-contained resin, or silicon, or applying a toner-releasing material such as silicon oil on the roller surface, has been considered to prevent the high-temperature offset. However, these techniques is not free from problems of durability, i.e. deterioration of the material caused by continuous use at a high temperature.
In the meantime, the technique of assigning the anti-offset property to toner itself has been considered, and more specifically, addition of another material composed of a substance insoluble to the resin to the toner as a component thereof, as is described Pulished Unexamind Japanese Patent Application 2-2578, has been proposed. However, if such an insoluble material is excessively add to enhance the anti-offset property, the toner becomes too cohesive at a high temperature. As a result, supply of toner from a container such as the toner hopper, will be very difficult. Further, if the fluidity of toner is lowered, the toner is not sufficiently stirred in the developer, suppressing charging on the toner. Such an uncharged toner is likely to cause fogging on an image, and is scattered in the copying device.